1. Field of the Invention
This invention relates to a disc cartridge, and more particularly to a disc cartridge in which a disc medium such as an optical disc, a photo-magnetic disc, a magnetic disc, a floppy disc or the like is received.
2. Description of the Prior Art
In general, a tray system or a cartridge system using a casing has been conventionally employed for protecting a floppy disc, a compact disc, a video disc or the like which is used for a digital-data storing unit, a video unit or the like from damage and dust to ensure its safety during the storage and operation. For this purpose, the casing is provided with a slidable shutter made of metal which is adapted to close a pickup inserting hole and/or a drive shaft inserting hole of the casing and to open these respective holes when the system is in use.
Such a shutter generally comprises a metal plate formed into a U-shape. For this purpose, the metal plate is subjected to stamping and bending to make the shutter integral with a slider. Unfortunately, this process leads to waste of the metal material and makes manufacturing of the shutter very difficult. This construction of the conventional shutter causes a shutter operating pin to strike against it thus wearing and/or damaging the pin, so that dust is produced.
Another shutter is used which is formed into a U-shape by mounting a slider on a shutter body by means of screws. However, this causes the number of manufacturing parts to greatly increase, as well as making manufacturing of the shutter difficult due to integration of a metal plate into the shutter body by means of pressing and bending operations, resulting in a decreased productivity rate of the shutter.
In view of the above, a shutter of having a three-part structure has been proposed which comprises two shutter plate members and a slider connected to the shutter plates through engagement between respective projections and recesses provided at the slider and shutter plates, as disclosed in Japanese Utility Model Application Laying-Open Publication No. 63879/1984. Unfortunately, the proposed shutter has an important disadvantage of failing in smooth handling of a cassette with respect to a disc cartridge operating unit such as a recording and/or reproducing unit (hereinafter referred to as "cartridge operating unit"), because a shutter operating pin of the unit often strikes against the aforementioned engagement projections or recesses.
In general, such a shutter including a slider is slidably biased by a combination of a shaft and a coiled spring. For example, in a slider disclosed in Japanese Utility Model Application Laying-Open Publication No. 55266/1986, blocks for engagement are provided at two or more portions of the slider on both sides of a pickup inserting hole and a shaft arranged within a stroke width of the slider is tightly inserted into the blocks, thus supporting the slider. Such construction causes the blocks for engagement to necessarily pass over the pickup inserting hole when the slider is moved, and accordingly, a space is required to permit passing of the blocks. This causes the shutter to occupy a relatively large area in a disc cartridge, resulting in the failure to ensure a desired relative position of a pickup in a cartridge operating unit. Also, this leads to striking of the shutter against a shutter operating pin of the unit which prevents smooth loading and unloading of the cartridge with respect to the unit.
Accordingly, there has been a need to develop a disc cartridge which prevents wear and damage of the shutter operating pin and ensures a desired positioning of a pickup of a cartridge operating unit, as well as being capable of being readily assembled thus resulting in a significant increase in the productivity rate of the cartridge.